The invention relates to an apparatus for measuring the thickness of printed products that are transported with the aid of a conveying device along a guide arrangement, the apparatus comprising a measuring element that forms a measuring gap together with the guide arrangement and acts upon the printed sheets on the side facing away from the guide arrangement, wherein the measuring element is furthermore connected to an evaluation unit.
A device for measuring the thickness of printed products is disclosed in Swiss Patent Document CH-A-523 787. This device is provided with a sensing wheel and a thereto assigned counter wheel. The printed products to be measured pass between these two wheels. The sensing wheel is deflected corresponding to the thickness of the measured printed products. Printed products that are too thin or which miss one or more printed sheets can thus be detected and removed. The aforementioned device has proven itself in practical operations. However, with printed products composed of thin paper, the individual printed sheets can be displaced, relative to each other, as a result of squeezing. In addition, the movement of the printed products while passing between the two wheels can furthermore result in leaving undesirable marks during the measuring operation on products with sensitive surfaces. Since the wheels must be positioned extremely precisely and must be driven while the machines operate at fast speeds, this measuring device is comparatively expensive and involved.
U.S. Pat. No. 4,170,346 discloses a measuring device for the capacitive and thus contact-less measuring of printed products that pass through. However, a capacitive measuring is not precise enough for measuring thin printed products and the scattering is comparatively high.
European Patent Document EP-A-0 714 789 discloses a measuring device on a gathering and wire-stitching machine, which also uses a sensing wheel and an associated counter wheel. The movement of the sensing wheel perpendicular to the conveying direction is measured with the aid of a laser beam. However, this device also has the aforementioned difficulties.